Sweetened fruit-flavored beverages such as lemonade, limeade, grapeade, etc. are commonly sold to the consumer in the form of a frozen concentrate. Furthermore, many sweetened fruit-flavored beverages sold as ready-to-drink liquids are reconstituted locally from frozen concentrates. The frozen concentrate form is chosen so frequently because: (1) its reduced weight and volume reduces the cost of shipping and storage; and (2) it extends the shelf life of the beverage by retarding or eliminating microbial spoilage.
The extension of shelf life by maintaining the concentrates at common freezer temperatures of -5.degree. to 15.degree. F. (-21.degree. to -9.degree. C.) is widely used, but not widely understood. Bacteria, yeasts, and molds thrive at room temperature in aqueous sugar solutions having a neutral pH. Unless one or more precautions are taken, the growth of microbes can rapidly increase to the point where the sweetened fruit-flavored beverage concentrate is unfit for human consumption.
One precaution for extending shelf life is to aseptically pack the concentrate in a sealed container. Aseptic packing requires a prolonged treatment at relatively high temperatures which frequently adversely affects the flavor and texture of the concentrates. Accordingly, this method is rarely used.
A second method of extending the shelf life of a concentrate is to formulate it so it exhibits a low water activity. Water activity is the ratio of the vapor pressure of water in a material to the vapor pressure of pure water at the same temperature. It is known that microorganisms have limits on their ability to prevent the loss of water from their cells. If the water activity of their environment is too low, the cells cannot regulate the water loss and either become dormant or die. For example, few bacteria can survive at water activities less than about 0.85, few yeasts can survive at activities less than about 0.80, and few molds can survive at activities less than about 0.75. This method of extending shelf life has not generally been employed because excessive drying and very low moisture levels have been required to reduce the water activity of a concentrate to less than about 0.8.
A third method of retarding or eliminating microbial growth is to add one or more preservatives to the concentrate. The most common preservatives used in fruit juices are the potassium and sodium salts of sorbic, benzoic, and sulfurous acids. However, these preservatives impart objectionable flavor at higher concentrations, especially at an acidic pH. Therefore, the use of preservatives to extend shelf life is not widely practiced.
Because of the disadvantages associated with the above methods of preserving concentrates, the most common method of preservation remains to maintain the concentrates at about -5.degree. to 15.degree. F. (-21.degree. to -9.degree. C.). This, of course, greatly increases the cost and inconvenience of shipping and storing the concentrates. Furthermore, at these temperatures, the concentrates are generally very hard. This hardness is, in turn, an inconvenience when the concentrate is diluted to form the drinkable beverage. It is usually necessary to thaw the concentrate at room temperature for 10 to 30 minutes to make it pourable and removable from its container before it is diluted.
Accordingly, there is a demand for a sweetened fruit-flavored beverage concentrate which does not require common freezer temperatures for preservation. There is also a demand for such a concentrate which remains pourable even at common freezer temperatures.
Kahn, U.S. Pat. No. 4,235,936, issued Nov. 25, 1980, discloses a microbiologically-stable beverage concentrate which is "semi soft" at freezer temperatures. The concentrate comprises about 15 to 55 percent water, sugar in a ratio to water of about 0.8 to 2:1, and flavoring. At least 10 percent of the sugar is fructose and at least about 50 percent of the sugar is either fructose or dextrose. The concentrate's microbial stability is said to be a result of its relatively low water activity of about 0.75 to 0.90. Kahn states that, although microbial stability is inversely proportional to water activity, the mouth-feel and taste of the concentrate are adversely affected at very low water activities and that water activities of about 0.90 to 0.93 are preferred. Example 1 of Kahn illustrates an orange juice concentrate. When a 600 ml. sample of the concentrate was frozen at 5.degree. F. (-15.degree. C.) in a graduated cylinder, then removed to room temperature and placed in a horizontal position, none of the concentrate flowed out of the cylinder after 1 minute and 125 ml flowed out after 3 minutes.